Cross-protection is a term used in immunology and vaccinology that refers to the ability of a vaccine or natural infection with one strain of a microorganism (such as a virus or bacteria) to provide protection against other, related strains. This occurs because the immune response elicited by the initial exposure also recognizes and targets certain common features present in the related strains.

In the context of vaccines, cross-protection can be an important factor in designing broadly protective vaccines that can cover multiple strains or serotypes of a pathogen, thus reducing the need for individual vaccines against each strain. However, the degree of cross-protection can vary depending on the specific microorganisms and antigens involved.

It's important to note that cross-protection is not always complete or long-lasting, and additional research may be needed to fully understand its mechanisms and limitations.

A coronavirus that primarily infects rats is called "rat coronavirus." It is a type of virus that belongs to the genus Betacoronavirus, which also includes coronaviruses that can infect humans, such as SARS-CoV and MERS-CoV.

Rat coronavirus is closely related to coronaviruses that infect mice and can cause respiratory illness in rats. It is typically transmitted through direct contact with infected rats or their feces and urine. Rat coronavirus infection is not known to spread to humans or other animals outside of laboratory settings.

It's worth noting that the current global pandemic is caused by a novel coronavirus called SARS-CoV-2, which is distinct from rat coronavirus and other known coronaviruses that infect animals.

Cross reactions, in the context of medical diagnostics and immunology, refer to a situation where an antibody or a immune response directed against one antigen also reacts with a different antigen due to similarities in their molecular structure. This can occur in allergy testing, where a person who is allergic to a particular substance may have a positive test result for a different but related substance because of cross-reactivity between them. For example, some individuals who are allergic to birch pollen may also have symptoms when eating certain fruits, such as apples, due to cross-reactive proteins present in both.

Antibodies, viral are proteins produced by the immune system in response to an infection with a virus. These antibodies are capable of recognizing and binding to specific antigens on the surface of the virus, which helps to neutralize or destroy the virus and prevent its replication. Once produced, these antibodies can provide immunity against future infections with the same virus.

Viral antibodies are typically composed of four polypeptide chains - two heavy chains and two light chains - that are held together by disulfide bonds. The binding site for the antigen is located at the tip of the Y-shaped structure, formed by the variable regions of the heavy and light chains.

There are five classes of antibodies in humans: IgA, IgD, IgE, IgG, and IgM. Each class has a different function and is distributed differently throughout the body. For example, IgG is the most common type of antibody found in the bloodstream and provides long-term immunity against viruses, while IgA is found primarily in mucous membranes and helps to protect against respiratory and gastrointestinal infections.

In addition to their role in the immune response, viral antibodies can also be used as diagnostic tools to detect the presence of a specific virus in a patient's blood or other bodily fluids.